Means for regulating mass burning rate of solid propellants



S. WOLF Dec. 11, 1962 MEANS FOR REGULATING MASS BURNING RATE OF SOLID PROPELLANTS Filed April 5, 1960 INVENTOR SAUL WOLF 249W ATTORNEYS.

United State The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to the control art and is more particularly concerned with a method and an apparatus for regulating the mass burning rate of a solid propellant.

I The motor of a missile such as torpedo, underwaterto-air or surface missile, or air or surface-to-underwater missile, may be operated at varying depths of water and heights of air. Accordingly, the ambient pressure or back pressure against which the motor operates may vary from less than atmospheric to several times atmospheric pressure during one flight of the missile. At high back pressures, the mass burning rate must be high while at lower ambient pressures, the mass burning rate must be relatively low to optimize the operation of a given missile.

In the past, two modes of regulation have been employed to control the rate of burning of solid propellant at a level dictated by the requirements of the system utilizing the propellant. The first of these is to match the propellants linear burning rate pressure exponent as closely as possible to the mass rate of burning changes required because of back pressure variations; the second is to burn the propellant at the maximum expected mass rate requirement for required thrust and to dump the excess when the actual mass rate requirement is less than the expected maximum. Since the first method requires extreme precision in predicting the trajectory of the missile and requires that each missile follow the same trajectory and the second method is wasteful of propellant at low loads, these methods have met with but indifferent success in the past.

It is therefore an object of this invention to provide a process and a system for regulating the mass burning rate of a solid propellant.

Another object is the provision end-burning grain which does not require a bonded to the propellant charge or grain.

Still another object is to provide a solid propellant system wherein the temperature of the combustion prod ucts may be varied within predetermined limits.

A still further object is the provision of a system for burning a solid propellant at a controllable rate from free burning to end burning.

I These and many other objects will become more readily apparent when the following specification is read in conjunction with the attendant drawing wherein like numerals designate like or similar parts throughout the various views and in which:

FIGURE 1 illustrates a propellant system constructed in accordance with the principles of this invention imme diately prior to ignition of the propellant; and

FIGURE 2 illustrates a propellant system as in FIG- URE 1 with certain parts omitted and at a time when the propellant is free burning.

Referring now to FIGURE 1, the missile 11 is propelled by the burning of a solid propellant grain 12, disposed within and adapted to slide axially through a bore 13 fixed in the missile.

A guide is affixed to one end of the grain to prevent the grain from cocking or binding in bore 13 as the combustion of the grain nears completion and the diameter to length ratio becomes larger than that which sound of a solid propellant fixed inhibitor dfifi'hfim Patented Dec. 11, 1962 engineering practice would dictate for a piston sliding in a cylinder.

As is apparent from the drawing, bore 13 is open at one end and at the opposite is connected to a source 14 of high pressure fluid by conduits 15 and 15 and a flow divider shown schematically at 16. The flow divider may be an electrically operated three-way valve or the like while source 14 may preferably be a high pressure positive displacement pump; in any event that portion of the fluid which is not directed to bore 13 by divider 16 is diverted and returned to the inlet of the source 14 via conduit 18. It may be desirable to provide a reservoir 17 or the like about equal in capacity to the volume of bore guide 13 and which is also connected to the inlet of source 14. A control mechanism 19 is provided to alter the proportion of the fluid flowing into bore guide 13 via conduit 15 or to recirculate the fluid through conduit 18 Mechanism 19 may emit an electrical signal similar to a conventional speed control signal as in a torpedo.

A jacketed chamber 21 is fixed at the open end of bore 13 and provides a free burning space 22 contiguous thereto. A portion 23 of chamber 21 is constructed of a porous or fibrous metal or ceramic or other material and forms a continuation of the wall of bore 13. Within the jacket of chamber 21 is disposed pressurized liquid inhibitor 24 which may be water. The inhibitor flows from any suitable source via coduit 31 into jacketed chamber 21 and through the porous wall portion 23 to form a continuous film on the grain 12 to prevent free burning of the grain within bore 13.

At one end of plenum 21 is formed a conduit 25 which may lead to a nozzle turbine or similar device for utilizing the energy of the burning propellant and shown schematically at 26.

Prior to ignition of charge 12 it occupies the position indicated in FIGURE 1 and a portion of the bore guide to the left of grain 12 is filled with fluid 27 which like the inhibitor may be water. The 0 rings 28 in bore 13 prevent cocking or binding of the grain in the bore guide and prevent inhibitor 24 or pressure fluid 27 as the case may be from leaking between the charge and the interior of guide 13.

The propellant grain is initiated by ignition of a squib 29 which is disposed against one end of the grain and which is ignited by any suitable means (not shown). The grain commences to burn at the surface of its exposed end. Source 14 provides fluid rat a rate suflicient to displace charge 12 to the right, as seen in the drawing, at a speed equal to or greater than the linear burning rate of the propellant. Accordingly, the burning surface of the charge remains external of the bore guide. In the event, for example, that the external back pressure increases thereby requiring a higher optimum mass burning rate, divider 16, upon receipt of a signal from control mechanism 1? which has sensed this change and developed a signal in accordance with this change of condition, increases the rate of fluid flow through conduit 15 and into bore 13. Thereupon, the grain moves axially within the bore to the right as seen in the drawing at a rate exceeding its linear burning rate so that it protrudes into the free burning space and combustion of the grain takes place at all exposed surfaces thereof. The inhibitor flows through the porous wall 23 and onto the grain at 2 rate suflicient to prevent the combustion at the grair surface from progressing within the bore guide on the surface of the grain. The mass burning rate at any time is the product of the linear burning rate multiplied b3 the total surface area of the grain exposed within the combustion chamber external of the bore guide. As the rate of advance of the grain into the bore chamber is increased beyond the minimum rate, which is equal to the linear burning rate of the propellant, the grain ti;

a is being advanced faster than it is being consumed at the linear burning rate. The result of this is to increase the length of the free burning grain within the chamber; the increased length results in more burning area within the chamber and thus a greater mass burning rate is effected. The combustion is, therefore, always under control, even when the grain is free burning in space 22.

In the event that it becomes desirable to decrease the temperature of the combustion products, the inhibitor flow rate may be increased. In such a case, the inhibitor serves to dilute the combustion gases and lower gas temperature as well as to prevent burning within the bore.

From the foregoing, it should be apparent to those skilled in the art that this invention provides a novel system for regulating the mass burning rate of a propellant grain from end-burning to free-burning wherein the plastic inhibitor normally incorporated into the grain may be dispensed with and the temperature of the combustion products may be selectively varied. If convenient, the axial motion of the grain may be attained by any suitable means, hydraulic or mechmical, such for example as a jack screw type arrangement. All that is required is that the rate of movement of the grain can be accurately controlled.

This invention is not to be construed as limited in any way by the foregoing illustrative example but the invention may be practiced in Ways other than specifically described in the specification within the terms of the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a propulsion system for a missile the improvement which comprises; a bore Within a missile and having an open end and a porous wall portion adjacent to the open end; a chamber afiixed to said bore at the open end thereof and defining a free burning space contiguous thereto; a solid propellant grain slidably disposed in said bore, means for igniting said grain at the open end of said bore; a pressurized liquid inhibitor in communication with the porous wall for flow therethrough thereby to prevent burning of the surface of the grain within the bore; and means for advancing said grain into the free burning space.

2. A propulsion system for a missile comprising; a bore within a missile and having an open end; a conduit connected to said bore at the end thereof opposite from the open end; a solid propellant grain slidably disposed in said bore, means for applying a liquid inhibitor to the,

surface of said grain adjacent the open end of said bore for inhibiting the burning of the surface of said propellant grain therein; pressurized liquid supply means connected to said bore by said conduit to deliver high pressure liquid into said bore and against said grain to axially slide the grain through said bore; and means disposedbetween said supply means and said bore for regulating the flow of liquid into said bore guide thereby to control the rate of sliding movement of the grain.

3. In a propulsion apparatus, an open ended cylindrical bore including a porous wall portion adjacent to the open end thereof, a jacketed chamber affixed at the open end of the bore at the porous wall portion and defining a free burning space adjacent thereto, an uninhibited solid propellant grain slidably disposed within said bore, means for igniting said propellant grain within the free burning space, pressurized liquid supply means for delivering liquid into said bore and displacing said grain into said free burning space, said liquid supply means being connected to the end of said bore opposite from said open end, adjustable means connected to said supply means for regulating the rate of delivery of the liquid into the bore, and means supplying a liquid inhibitor into the jacketed portion of said chamber and through the porous wall portion of said guide thereby to inhibit combustion of the surface of the grain within the bore and to control the temper-attu'e of the combustion gases.

References Cited in the file of this patent UNITED STATES PATENTS 2,703,960 Prentiss Mar. 15, 1955 2,971,097 Corbett Feb. 7, 1961 2,988,879 Wise June 20, 1961 FOREIGN PATENTS 582,621 Great Britain July 13, 1943 

